The field of the present invention relates to data reading systems and methods of data reading, and in particular a pre-alignable and interchangeable optics module for use in a data reading system.
Data readers such as bar code scanners, are used in a wide range of retail, commercial and industrial applications to read optical codes on numerous items for purposes such as point of sale (POS) check-out, product inventory and item tracking. Scanners may generally be classified into two categories: fixed scanners, such as counter top scanners for checkout applications, and hand held scanners, which are used for retail checkout as well as many inventory and tracking applications.
Regardless of the application, laser beam scanners typically have an optical system composed of a low power laser source which projects a laser beam; mirrors to direct the laser beam; beam forming devices such as focussing lens or apertures to develop the correct laser beam diameter; a scanning mechanism such as a drive assembly comprising a rotating polygon mirror, a reciprocating mirror, or a holographic element to scan the laser beam at a package label and illuminate the bars and spaces of a bar code symbol; a collection element such as a lens or mirror to gather the diffused light reflected from the label; and a detector to convert the reflected light into an analog signal for subsequent digital decoding.
Laser beam scanners have been manufactured such that the scanner""s final assembly involved directly attaching the various optical components on the scanner housing in a plurality of assembly steps or attaching the components to scanner subassemblies for subsequent assembly to the scanner housing. Regardless of the assembly sequence, in the past, there were a number of optical elements made adjustable at final scanner assembly, such as the routing or pattern mirrors, by which the laser light was aligned. These mirrors were required to be adjusted after assembly of the subassembly or even after final scanner assembly so that a desired scan pattern would be produced for exiting the scanner. Also, the adjustments were necessary to optically align the returning light reflected from a bar code symbol with the scanner""s collection lens and photodetector for gathering the optical data. To achieve the necessary alignment, adjustments were typically made on two to six mirrors after final assembly. For example, in a scanner such as the Magellan(copyright) SL scanner of PSC Inc. of Eugene, Oreg. the motor/polygon scan mirror assembly and the VLDM assembly are mounted in fixed, pre-aligned positions, but both a routing mirror and beam splitter disposed in the beam paths between the VLDM and the polygon mirror are each mounted on respective bendable metal frames which may be bent providing optical alignment adjustment after final assembly.
Furthermore, in some scanners, if the laser source becomes inoperative after the scanner""s final assembly alignment, the scanner is repaired by replacing the defective light source after which another optical alignment has to be performed. The optical alignment following replacement of the defective laser is necessary because the pointing error of one laser source to another laser source is not the same. As a result, after the laser is replaced with a new unit, either the desired scan geometry exiting the scanner is lost or the returning light is no longer aligned with the collection lens and the photodetector, or both.
The pointing error, which is the deviation of the projected laser beam from perfect, varies from one laser diode to another because, for example, the chip location inside the diode casing is not consistent. The imperfect position and concentricity of the focussing lenses forming the laser beam may further aggravate the pointing error variance between laser diodes. Furthermore, it is currently too expensive to design and consistently manufacture a laser source, such as a laser diode or laser tube, having a sufficiently small pointing error so as to eliminate the need to perform the scanner assembly alignment.
In sum, where the light source fails after final scanner alignment, a second scanner assembly alignment has been necessary after replacing the defective laser source. As a result, if a scanner unit fails in the field, it must either be returned to the factory for servicing or the optics of the scanner must be aligned in the field. Replacing a defective light source in the field is difficult because special tooling and a trained technician are required. Consequently, to date, replacement of defective laser sources has been both costly and time consuming.
In a preferred embodiment of the invention, an integrated optics module capable of pre-alignment is provided. The integrated optics module is designed for use in an optical scanning system that includes a scanning mechanism for generating a scan pattern from a laser beam. By pre-aligning the optics module, the need for scanner re-alignment when components are changed in and out of the scanner is eliminated. As a result, if the laser source on an optics module fails, the optics module may be replaced with a new optics module and the scanning system will remain operational without the need for performing an optical alignment on the individual components of the system.
In another preferred embodiment, the optics module includes an optics block, a laser mounted on the optics block, routing optics mounted on the optics block in the path of the laser beam emitted from the laser, a collection element such as a collection lens disposed on a surface of the optics block, and mounting fixtures. The mounting fixtures are designed to removably mount the optics block to the scanner housing in a fixed position so that the optics block has a predetermined orientation in relation to the scanning mechanism.
In another preferred embodiment, a printed circuit board, such as the analog board, having a photodetector mounted thereon is mounted on the optics block to insure that the collection element is aligned with the photodetector from one optics module to another.
Further objects, features, and advantages of the invention will be better understood from the following description considered in connection with the accompanying drawings in which various embodiments of the invention are illustrated by way of example.